1. Field of the Invention
The present invention relates to a background image acquisition method, a video game apparatus, a background image acquisition program, and a computer-readable medium containing a computer program that are implemented for a video game using an input image supplied by a camera.
2. Description of the Related Art
In recent years and continuing, a video game using an input image supplied by a camera is becoming increasingly popular. In this type of video game, for example, an image of the posture of a player is captured by a camera and the captured image is composited with an image such as a button item. The composite image may be displayed on a monitor, and when the hand (arm) of the player is moved over the button item, the button item may respond to the movement and instigate an action, for example. In this case, a command input may be made solely based on the image captured by the camera, and a game controller (control pad operated by the hand) may not be necessary for controlling the playing of a game.
In the prior art, this type of video game relies on a technique involving acquisition of a so-called frame difference and recognizing movement within a portion when a change that is greater than a predetermined level is detected in this portion. The frame difference refers to the difference between an immediately preceding frame and the current frame (i.e., difference in pixel information between pixels of the frames, the pixel information corresponding to a color signal in RGB format, a brightness signal in YUV format, a signal representing the difference between a brightness signal and a red color signal, or a signal representing the difference between a brightness signal and a blue color signal, for example). Also, in the prior art, one or more images such as button items are arranged on a monitor screen for controlling the playing of a game and an image of a hand or some other movable part is arranged to be moved over the button items to realize game operations.
In the technique relying on detection of movement of an image of a hand over one or more button items as is described above, the image of the player has to be displayed on the monitor screen. Therefore, a display screen such as a CG (Computer Graphics) screen representing features of the game may not be displayed on the entire monitor screen, and the game content may be degraded. Also, in this technique, operations are limited since an action may only be induced by activating the button item; that is, more detailed operations such as successively controlling the movement or position of a game character, for example, that may be realized by an analog stick type game controller (i.e., a game controller that is capable of outputting operations information including intermediate values by tilting a stick-type operations unit in up/down/left/right directions using fingers) may not be realized.
Accordingly, in order to enable more detailed game operations, a technique is proposed for detecting the pose of a player based on the positioning of the hand of the player in addition to inducing action by moving the hand over a button item, for example. In this case, some poses may not be detected based merely on the frame difference as is described above, and in a case where the player remains still, the pose of the player may not be detected based on the frame difference. Accordingly, the concept of a so-called background difference is introduced. Background difference refers to a difference (i.e., pixel information difference) between a background image that does not include an image of the player and a current image that includes the image of the player. According to an example, the background difference may be acquired and a portion at which a change exceeding a predetermined level is detected may be determined to correspond to a portion at which the hand of the player is positioned.
By introducing the concept of background difference to the video game using an image supplied by a camera as is described above, a number of poses may be detected, and more detailed game operations may be performed. In such a case, the background image without the player being shown has to be captured and stored beforehand.
However, if the player is moved away from the camera in order to capture the background image, command input based on image recognition (i.e., inducing action by moving the hand of the player over a button item) may not be realized. Therefore, a game controller has to be used. However, this means that the advantageous feature of not requiring a game controller in this type of video game using an input image supplied by a camera may be lost.